Bladed rotor



Dec. 25, 1945. F. A. M. HEPPNER 2,391,623

BLADED ROTOR Filed Aug. 11, 194-4 2 Sheets-Sheet l Patented Dec. 25,1945 BLADED ROTOR Fritz Albert Max Heppner, land, assignor to ArmsLimited, Coventry,

Leamington Spa, Enstrong Siddeley Motors England Application August 11,1944, Serial No. 549,038 In Great Britain December 8, 1943 4 Claims.

This invention relates to a rotor having a pcripheral row of blades, thelatter carrying at their outer ends shrouds which form a ring and areinterlocked against relative radial and lateral movement-for example, asdisclosed in the specification of my co-pending U. S. Patent ApplicationSerial No. 549,039 filed August 11, 1944.

My main object is to reduce the maximum deflection in a shroud due tocentrifugal action.

In the accompanying sheets of drawings:

Figure 1 is a fragmentary, part-sectional, elevational view of acompound turbine rotor having shrouds according to the invention, onlytwo shrouds with thei associated blades being shown (and in elevation)whilst the portion of the rotor itself is shown as a section on the lineII of Figure 2;

Figure 2 is an elevational view of one of the shrouds, with itsassociated blades, taken from the right of Figure 1, the portion of therotor itself being in cross-section;

Figure 3 is a fragmentary plan of two shrouds when separated, and Figure4 is a fragmentary perspective view of one of the shrouds, indicating apreferred form of interlock such as that disclosed in the specificationaforesaid; and

Figure 5 is a diagram hereinafter described.

According to the invention the shrouds are offset in a circumferentialdirection relatively to the associated blades so as to reduce themaximum deflection in a shroud, due to centrifugal action, to a valuelower than if the shrouds were centrally placed with respect to theassociated blades. Preferably, each blade is connected to its associatedshroud approximately mid-way between the centre of the shroud and oneend, or preferably slightly nearer the said one end.

In this way, with a certain construction I can reduce the maximumdeflection from three thousandths of an inch to one thousandth of aninch. This is an important consideration if the bladed roto forms partof an internal combustion turbine plant in which, for example, therunning clearance is only approximately 30 thousandths of an inch.

In the construction shown, I2 indicates a rotor in which are secured theroots ll! of compressor blades H (the cross-section of which isindicated by the chain lines IS) in the manner disclosed in thespecification aforesaid, and I! are relativelythin, flat shroudscarrying externally turbine blades l8, the cross-section of which isindicated by the chain lines l9.

One end of a shroud has machined in it transverse slots 2|, 22 of whichone. 2|, is narrower than and imposed upon the other. The mating edge ofthe adjacent shroud has complementary projections 23 formed thereon, allas disclosed in the specification aforesaid. In this way, when theshrouds are brought together in the form of a ring, they are interlockedagainst radial or lat- I eral movement.

It is found that the centres of gravity of different sections of ablade, taken along the length of a blade, all lie substantially on aradial line such as that marked 25, this applying both to a compressorblade and to an associated turbine blade, such radial line passingcentrally through the blade root. According to the invention it passesnot through the centre of the shroud but to one side of the centre, andfor preference, and as shown, it intersects the shroud at a distancewhich is approximately 0.22 of the length of the shroud from one edge ofthe shroud.

The reason for this will be apparent from a consideration of Figure 5.in which the problem considered is that of a uniformly-loaded beam ofuniform section supported at an arbitrary point X where the load P isapplied. There is also a load Pl at each end of the beam, and a symmetrycondition (that the beam shall be identical in loading and deflection toa similar one on either side) necessitates the loads Pl at the two endsbeing equal and opposite, and the deflections, of the two ends from thepoint X where the load P is applied, equal. The support and the two endsare assumed to apply no bending moment to the beam. It is required tofind the best position of the point of support in order to minimiseeither or both the stress and the deflection.

The equal and opposite loads (Pl) on the ends may be determined by thestatical equilibrium of the beam for any fixed position of the point ofsupport. The bending moment diagram (due to centrifugal forces) may thenbe constructed and the deflections calculated, as shown for a typicalcase in the small diagrams. Normally, the bending moment has two maximumvalues, one at the point of support X (at a distance a from one end) andone between the point of support and the end furthest away, and thedistance between the two maximum bending moment points is /;L, where Lis the length of the beam. The former bending moment vanishes if thepoint of support is at one end, and the latter if it is exactly in thecentre. The variation of the two'for different positions of support isshown in the main diagram, marked Z. In this diagram the bending momentsare represented by a dimensionless factor 0 by dividing by the totalload and the length of the beam.

The small diagram of a typical deflection curve shows the deflection h,between the point of support and the point furthest away from it, in adirection perpendicular to the beam. This dimension is important in thecase considered because the distorted shroud must move past anundistorted one (in the adjacent row of blades, which are stationary),and this distance must be added to the centrifugal expansion of therotating compressor blade to give the minimum clearance. The main graph,marked "deflection h, shows the variation of this deflection,represented again by a dimensionless factor. according to the positionof the support.

The bending moment diagram Z shows that for a beam of uniform sectionthe stresses are least when the point of support is 0.15 of the distancealong the beam. This stress occurs at two places, and any change ofposition of the support would cause one of them to increase, althoughthe other would decrease. 7

The minimum value of the deflection is seen to occur when the point ofsupport is 0.22 of the distance along the beam. Thus according towhether stress of deflection is most critical, the optimum point ofsupport will lie somewhere between these two values.

It should be understood that the shroud is stiffened up by the integralinner and outer blades the sections of which, at the shrouds, areinclined to one another, and this reduces the effective length of thebeam and would, in point of fact, modify the shape of the curves shown.

What I claim as my invention and desire to secure by Letters Patent ofthe United States is;

1. A rotor having a peripheral row of blades,

said blades carrying at their outer ends shrouds.

which form a ring and are interlocked against relative radial andlateral movement, an outer row of blades carried externally by saidshrouds, the shrouds being offset in a circumferential directionrelatively to the associated blades of the inner row so as to reduce themaximum deflectioninashroudduetocentrirugalactiontoa value lower than ifthe shrouds were central with respect to the associated blades of theinner row.

2. A rotor having a peripheral row of blades, said blades carrying attheir outer ends shrouds which form a ring and are interlocked againstrelative radial and lateral movement, an outer row of blades carriedexternally by said shrouds, th blades of each shroud being arranged sothat the lines through the centres of gravity of different sections ofthe blades are coincident, the shrouds being offset in a circumferentialdirection relatively to the associated blades so as to reduce themaximum deflection in a shroud due to centrifugal action to a valuelower than if the shrouds were central with respect to the associatedblades.

3. A rotor having aperipheral row of blades, the latter being fast attheir outer ends with shrouds which form a ring and are interlockedagainst relative radial and lateral movement, an outer row of bladeswhich are individually fast with the shrouds and respectively alignedwith the blades of the inner row, the shrouds being oflset in acircumferential direction relatively to both the associated blades suchthat the line through the centres of gravity of different sections ofeach blade is approximately mid-way between the centre of the shroud andone end.

4. A rotor for an intemal-combustion turbine plant having a peripheralrow of compressor' blades, the latter carrying at their outer endsshrouds which form a ring and are interlocked against relative radialand lateral movement, a row of turbine blades carried externally by theshrouds, the shrouds being oflset in a circumferential directionrelatively to the associated compressor blades such that the linethrough the centres of gravity of different sections of each compressorblade is at a distance from one end of the shroud which is between 0.2and 0.25 of the circumferential length of the shroud.

FRITZ ALBERT MAX HEPPNER.

